PET Scan

Contents

Procedure Information

How should I prepare for the procedure?

PET is usually done on an outpatient basis. Your doctor will give
you detailed instructions on how to prepare for your examination. You
should wear comfortable, loose-fitting clothes. You should not eat for
four hours before the scan. You will be encouraged to drink water. Your
doctor will instruct you regarding the use of medications before the
test.

Note: Diabetic patients should discuss specific diet guidelines
to control glucose levels during the day of the test.

What does the equipment look like?

You will be taken to an examination room that houses the PET
scanner, which has a hole in the middle and looks like a large,
doughnut. Within this machine are multiple rings of detectors that
record the emission of energy from the radioactive substance in your
body. While lying on a cushioned examination table, you will be moved
into the hole of the machine. The images are displayed on the monitor
of a nearby computer, which is similar in appearance to the personal
computer you may have in your home.

How does the procedure work?

Before the examination begins, a radioactive substance is produced
in a machine called a cyclotron and attached, or tagged, to a natural
body compound, most commonly glucose, but sometimes water or ammonia.
This process is called radiolabeling. Once this attached substance is
administered to the patient, the radioactivity localizes in the
appropriate areas of the body and is detected by the PET scanner.

Different colors or degrees of brightness on a PET image represent
different levels of tissue or organ function. For example, because
healthy tissue uses glucose for energy, it accumulates some of the
radiolabled glucose, which will show up on the PET images. However,
cancerous tissue, which uses more glucose than normal tissue, will
absorb more of the substance and appear brighter than normal tissue on
the PET images.

Scientifically speaking, the radioactive substance decay leads to
the ejection of positive particles called positrons. A positron travels
about one to two millimeters before colliding with an electron. The
collision results in a conversion from mass to energy, resulting in the
emission of two gamma rays heading off in exact opposite directions.
Special crystals, called photomultiplier-scintillator detectors, within
the PET scanner detect the gamma rays. The scanner's special camera
records the millions of gamma rays being emitted, and a connected
computer uses the information and complicated mathematical formulas,
called algorithms, to map an image of the area where the radioactive
substance has accumulated.

How is the procedure performed?

A nurse or technologist will take you into a special PET examination
room. You will lie down on an examination table and be given the
radioactive substance as an intravenous injection (although, in some
cases, it will be given through an existing intravenous line or inhaled
as a gas). It will then take approximately 30 to 60 minutes for the
substance to travel through your body and be absorbed by the tissue
under study. During this time, you will be asked to rest quietly in a
partially darkened room and to avoid significant movement or talking,
which may alter the localization of the administered substance. After
that time, scanning begins. This takes an additional 30 to 45
minutes.

Some patients, specifically those with heart disease, may undergo a
stress test in which PET scans are obtained while they are at rest,
then after undergoing the administration of a pharmaceutical to alter
the blood flow to the heart.

Usually, there are no restrictions on daily routine after the test,
although you should drink plenty of fluids to flush the radioactive
substance from your body.

What will I experience during the procedure?

The administration of the radioactive substance will feel like a
slight pinprick if given by intravenous injection. You will then be
made as comfortable as possible on the examination table before you are
positioned in the PET scanner for the test. You will be asked to remain
still for the duration of the examination. Patients who are
claustrophobic may feel some anxiety while positioned in the scanner.
Also, some patients find it uncomfortable to hold one position for more
than a few minutes. You will not feel anything related to the
radioactivity of the substance in your body.

Who interprets the results and how do I get them?

Patients undergo PET because their referring physician has
recommended it. A radiologist who has specialized training in PET will
interpret the images and forward a report to your referring physician.
It usually takes one to three days to interpret, report, and deliver
the results.

What are the benefits vs. risks?

Because PET allows study of body function, it
can help physicians detect alterations in biochemical processes that
suggest disease before changes in anatomy are apparent on other imaging
tests such as CT or MRI scans.

Because the radioactivity is very short-lived,
your radiation exposure is extremely low. The substance amount is so
small that it does not affect the normal processes of the
body.

The radioactive
substance may expose the fetus of patients who are pregnant or the
infants of women who are breast-feeding to the radiation. The risk to
the fetus or infant should be considered related to the potential
information gain from the result of the PET
examination.

What are the limitations of Positron Emission
Tomography?

PET can give false results if a patient's chemical balances are not
normal. Specifically, test results of diabetic patients can be
adversely affected because of blood sugar or blood insulin levels.

Also, because the radioactive substance decays quickly and is
effective for a short period of time, it must be produced in a
laboratory near the PET scanner. It is important to be on time for the
appointment and to receive the radioactive substance at the scheduled
time. PET must be done by a radiologist who has specialized in nuclear
medicine and has substantial experience with PET. Most large medical
centers now have PET services available to their patients. Medicare and
insurance companies cover many of the applications of PET, and coverage
continues to increase.

Finally, the value of a PET scan is enhanced when it is part of a
larger diagnostic work-up. This often entails comparison of the PET
scan with other imaging studies such as CT or MRI.

What are some common uses of the procedure?

PET scans are used most often to detect cancer and to examine the
effects of cancer therapy by characterizing biochemical changes in the
cancer. These scans are performed on the whole body. PET
scans of the heart can be used to determine blood flow to the heart
muscle and help evaluate signs of coronary artery disease.
Combined with a myocardial metabolism study, PET scans differentiate
non-functioning heart muscle from heart muscle would re-establish
adequate blood flow. PET scans of the brain are used to evaluatae
patients who have memory disorders of an undetermined cause; who have
suspected or proven brain tumors; or who have seizure disorders that
are not responsive to medical therapy, and therefore, are candidates
for surgery. PET is usually done on an outpatient basis.

Who interprets the results and how do I get them?

Patients undergo PET because their referring physician has
recommended it. A radiologist who has specialized training in PET will
interpret the images and forward a report to your referring
physician. It usually takes one to three days to interpret,
report, and deliver the results.

What must be done prior to the scan?

All patients are to check in at the Radiology Department Reception
Area located on the first floor of the University Hospital at the
designated appointment time. You may want to allow extra time for
parking. Your procedure may involve the use of a drug that is specially
ordered for your test. If you are unable to keep this appointment
for any reason, we ask that you call our Scheduling Office at
(434) 924-9400 at least 24 hours prior to
your appointment if possible. If you are going to be late, please
call us at that same number.